1. Field of the Invention
The present invention relates to an improved engine revolution frequency control apparatus having an overspeed governing capability.
2. Description of Background Art
An engine has a prescribed allowable maximum revolution frequency, and operation exceeding this allowable maximum revolution frequency must be avoided in terms of protection of the engine. As an overspeed prevention technology, xe2x80x9cthe engine control apparatusxe2x80x9d disclosed in JP-A-9-126019 is known. This technology is such that a control unit suppresses and controls the engine revolution frequency when the pace of increase in engine revolution frequency reaches the prescribed value or larger.
The technology disclosed in the aforementioned patent gazette can prevent an abrupt increase in engine revolution frequency even when it occurs in the low speed area or medium speed area, because the pace of increase in revolution frequency is observed. However, since observation is made based on the pace of increase in revolution frequency, it is not able to detect that the engine revolution frequency is beyond the allowable maximum speed when the engine revolution frequency is increased relatively slowly.
The apparatus is adapted to restrain the engine revolution frequency when either the engine revolution frequency exceeds a prescribed value, or the pace of increase in revolution frequency exceeds a prescribed value is detected. However, the control system becomes complex, and restraint control of the engine is not implemented sufficiently to maintain the ride quality of the vehicle or the boat.
Accordingly, it is an object of the present invention is to provide an engine revolution frequency control apparatus in which a preferable overspeed governing capability can be achieved.
In order to solve the problem described above, the engine of the present invention includes a revolution frequency detecting means for detecting the engine revolution frequency and an engine control unit for controlling the engine revolution frequency. The engine control unit is provided with an overspeed governing capability that starts restraint control for restraining rotation when the engine revolution frequency detected by the engine revolution frequency detecting means exceeds a first threshold value during acceleration, and terminates restraint control when the engine revolution frequency is decreased to the value below a second threshold during deceleration, and the second threshold value of the engine revolution frequency is set to be higher than the first threshold value.
Restraint control of the engine revolution frequency may be realized by cutting or reducing supply of fuel, leaning of air-fuel mixture, delaying of the ignition timing, or reducing the number of times of ignition.
Even when restraint control is started by the fact that the engine revolution frequency exceeds the first threshold value, increase in revolution frequency continues for a while due to inertia. After that, when restraint control comes on or when a large load is exerted thereon, the engine revolution frequency starts to be reduced. When a large load is exerted, even when terminating restraint control at a certain threshold value, reduction of the engine revolution frequency continues for a while, which result in significant drop of the engine revolution frequency.
Therefore, according to the present invention, the second threshold value at which the restraint control is terminated is set to a value higher than the first threshold value at which restraint control of the engine revolution frequency is started, so that drop of the engine revolution frequency may be reduced.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.